Effects of raloxifene therapy on the anticoagulant system in postmenopausal women

Background Raloxifene therapy is associated with a three-fold increase in the risk for venous thromboembolism, however, its effects on the hemostatic system in postmenopausal women have not been well defined. Objective To determine the effects of raloxifene therapy on the levels of natural anticoagulant proteins in postmenopausal women. Methods Sixteen healthy postmenopausal women were enrolled in this prospective longitudinal study. The patients were treated with raloxifene hydrochloride (60 mg/day) for a period of 6 months. Antithrombin and protein C activities and protein S antigen levels were measured in all users at baseline, and after 1, 3 and 6 months of treatment. Statistical analysis included one-way analysis of variance (ANOVA) and the Bonferroni test for Multiple comparisons among the study periods. Results Statistically significant 5.1% and 6.5% reductions of plasma antithrombin activity were observed at 3 and 6 months of therapy, respectively (P < 0.05). Compared with baseline, raloxifene did not significantly affect protein C activity or protein S level. Conclusions The results of this prospective study show for the first time that raloxifene use is associated with a significant reduction in plasma antithrombin activity. This effect may contribute to a procoagulant state and partly explain the increased risk of venous thromboembolism in raloxifene users.